The present invention relates to a pivoting lever arm mechanism utilized in transmitting reciprocal linear motion and/or force by pivoting about a fulcrum pivot point intermediate the ends of the lever arm, and more particularly to a lever arm of this sort having the capability of varying the ratio of lengths of moment arms from respective ends of the lever arm about the fulcrum pivot point there between.
The instant invention may be utilized in mechanical devices wherein reciprocal linear motion is to be transmitted (1) in a different direction, (2) in a specifically defined ratio of distances of linear movements, or (3) in instances wherein the linear motion causing movement of the lever arm is provided directly by the rotational movement of a cam device having one or more lobes thereon, or wherein the linear motion is provided by a lever, piston or other power input device, the effect of which is to reciprocally urge the end of the lever arm in an arcing movement pattern about the fulcrum pivot point.
In the field of overhead valve internal combustion engines, valve rocker arms have been constrained to reciprocal rotational movement about a fixed fulcrum point. Because this fulcrum point is fixed relative to the fixed location of the engine valves and camshaft and/or pushrods, the amount of valve opening is constant throughout the entire range of engine speeds and engine load conditions. Therefore, it has been considered highly desirable to provide a means whereby the amount of valve opening may be varied and controlled during engine operation in response to variations in engine load demand. Specifically, it has been desirable to provide a device for permitting the selective increase in valve opening amount in relation to increased engine revolutions per minute (hereinafter xe2x80x9cRPMxe2x80x9d) and additionally, decrease the amount of valve opening at engine speeds below the optimum power peak point designed into the specific engine camshaft.
At engine speeds below this optimum power peak, a decrease in amount of valve opening proportional to RPM prevents the camshaft from xe2x80x9cloadingxe2x80x9d and, therefore, provides greater torque at engine speeds in this below peak range. In a similar manner, at engine speeds above this power peak, an increase in amount of valve opening proportional to RPM provides greater power output in this above power peak range. The end result is to effectively broaden the optimum power peak curve, by effecting a power peak that actually shifts as a function of valve opening, which is related to actual engine RPM. In this manner, increased fuel economy is obtained at all engine speeds because the actual amount of valve opening is optimum across essentially the entire speed range for the specific camshaft design.
The present invention has specific application to internal combustion engines, wherein the lever arm takes the form of the rocker arm on overhead valve type engines and the reciprocating linear motion is transmitted from a rotating cam either directly to the rocker arm or indirectly to the rocker arm through a pushrod member. The rocker arm pivots about a fulcrum point so that the reciprocating arcing motion transmitted to one end of the rocker arm is passed therethrough, via oscillatory rotation about the fulcrum pivot point, to the other end of the rocker arm which engages the stem of a valve situated within the engine head to thereby selectively open the valve to permit intake and exhaust gases to pass there around.
The present invention provides the means whereby the ratio of the distance of reciprocal arcing movement of the end of the rocker arm that engages the camshaft or pushrod relative to the fulcrum pivot point, to the distance of arcing movement of the end of the rocker arm that engages the valve stem may be varied in response to variations in engine load requirements while the engine is operating.
It should be apparent that the present invention has applications other than rocker arms for internal combustion engines. However, for purposes of explanation, it will be described and explained with reference to internal combustion engine valve opening mechanisms.
The present invention provides a novel variable fulcrum rocker arm mechanism that may be used with an overhead valve type internal combustion engine for shifting the fulcrum point about which the lever arm pivots relative to the opposing ends of the lever arm. The invention will be described in terms of a valve opening rocker arm which is retained in place relative to the position of the valve stem and pushrod, or point of contact of a camshaft acting on the rocker arm. The rocker arm incorporates an essentially elongate through aperture through which the fulcrum rod is functionally positioned, so that the rocker arm may pivot about the fulcrum rod.
The rocker arm utilizes a shaft with underbelly splines that mate with corresponding splines in the lower trunnion section of specially designed rocker arms. Specific positioning of this splined shaft changes the fulcrum point. The movable fulcrum enables a change of the relative arc length of travel of each end of the rocker arm. In this manner, the amount of valve opening can be altered and controlled for any given constant amount of pushrod reciprocal movement or camshaft lift.